Vízügyi Közlemények, 1996 (78. évfolyam)
1. füzet - Szlávik L.-Varga M.-Váradi J.: A vízkár-elhárítási védekezési munkák országos irányításának tapasztalatai az 1995. decembere és 1996. júniusa közötti időszakban
28 Szl ávik L — Varga M. — Väradi J. that of the new law on water management by the Parliament. This new law was became into force on the 1st of January, 1996. It regulates the activities of the prevention of water damages, specifying the tasks of all interested parties item-by-item. Finally the flood defence activities had to be performed by the very recently rearranged water management organization and with the availability of a much reduced staff. The authors present and illustrate the extreme character of the floods (Fig.s 1—2 and Table I.), the extent of excess water inundations (Fig. 5.), the staff and equipment utilized for the defence operation (Figures 3. and 6., Table II.) and they summarize the experiences of the national level management of these operations in the light of these data. The extremity of the flood of December 1995 - January 1996 was characterized, in addition to maximum levels and durations exceeding those ever observed, by very difficult defence work along the frozen and snow covered levees. The first and most important experience was that the first trial of the reorganized district water authorities has been a success, even with their much reduced staff and equipment, and the floods were released without levee failure and without considerable damages to property. In the Körös water system, where the most critical floods occurred, the success was facilitated to a great extent by the timely and well planned opening of the emergency flood storage basins of Mályvád and Mérges. Experiences gained in the Körös system have already been utilized during the flood of April 1996 of the Rába river valley, where preparations were made for the opening of the emergency storage basins along the river Rába, due to the intensity of flooding. Lower than expected water stages, however, did not necessitate the actual opening of the emergency flood storage basins. Another important experience of the floods of December 1995 — June 1996 was that the most critical conditions occur at relatively low dikes made of compact clay, which are prone to the occurrence of dangerous cracks and fissures (such as those of the Upper Tisza River and the Körös River system). Seepage and excessive wetness (soaking) caused the main problems at the levees of the Rába river, that have not been subject to floods for nearly three decades, evens at sites where such problems have never occurred before. The management of flood defence operations was hindered partly by the transitional legal situation (Until the 31st of December 1995 the law No. LV. of 1964 had been in force, while the new law No. LVI1 of 1995 entered into force on the 1st of January 1996) and partly by the unexperienced condition of calling in "external forces" for the defence operation along the flood levees. Nevertheless, there were no serious disturbances in the activities and operation of the defence organization, as it might have been expected due to the much differing earlier experiences of the recently involved local governments (the mayors) and other agencies from that of the "Defence Committees" that coordinated the work at the level of state administration. The most important experience with the control of excess water inundation at local level was that, due to the lack of maintenance work, the condition of drainage canals and other facilities were deteriorated to such an extent that critical water stages were reached already at 5070% of the design flow of the canals. This resulted in the non-flexible operation of the drainage systems, with the meaning that excess water volumes were released much slower than before, even at higher than usual water levels. The consequence of this was that pumping stations could only be operated intermittently, that is the discharge capacities of canals were not in harmony with those of the pumping stations. Economic problems have also been encountered during the excess water drainage operations. Namely, there are no measures or calculation methods that could provide a basis for deciding whether a given excess water drainage operation is economical or not. Although costs can be relatively well defined there are no criteria or measures available to assess the benefit. As contrasted to this the water authorities must meet new expectations, according to which costs of the defence work must be proportional to the damage prevented. Regarding the experiences of local water damage prevention operations the authors classify the extreme rainstorms of May-June, 1996, as non-experienced natural phenomena. The return period
